Preparation of graded semiconductor films by the layer-by-layer assembly of nanoparticles

Abstract

This invention relates to the layer-by-layer assembly of graded semiconducting films by laying nanoparticles on a substrate in a sequence from smaller to larger sizes, which can be done economically and effectively. Layer-by-layer assembly (LBL) enables effective processing of semiconductor, metal, or metal oxide nanoparticle dispersions into functional advanced materials, which retain distinctive optical, magnetic and electrical qualities of size-quantized state of matter.

In the claims:  
     
         1 . A nanoparticle film comprising: 
 a first nanoparticle dispersion having a first luminescent maxima;    a second nanoparticle dispersion having a second luminescent maxima, wherein said second luminescent maxima is has a greater wavelength than said first luminescent maxima; and    wherein said first nanoparticle dispersion and said second nanoparticle dispersion form a graded media.    
     
     
         2 . The film according to  claim 1  wherein: 
 said nanoparticles are comprised of CdTe.  
 
     
     
         3 . The film according to  claim 1  wherein: 
 said first luminescent maxima is between approximately 496 and 505 nm; and  
 said second luminescent maxima is between approximately 530 and 545 nm.  
 
     
     
         4 . The film according to  claim 1  further comprising: 
 a third nanoparticle dispersion having a luminescent maxima of a greater wavelength than said second luminescent maxima.  
 
     
     
         5 . The film according to  claim 4  wherein: 
 said third nanoparticle dispersion has a luminescent maxima of between approximately 530-545 nm.  
 
     
     
         6 . The film according to  claim 4  wherein: 
 said third nanoparticle dispersion displays an orange luminescence.  
 
     
     
         7 . The film according to  claim 4  further comprising: 
 a fourth nanoparticle dispersion having a luminescent maxima of a greater wavelength than said third nanoparticle dispersion.  
 
     
     
         8 . The film according to  claim 7  wherein: 
 said fourth nanoparticle dispersion has a luminescent maxima of between approximately 605 to 620 nm.  
 
     
     
         9 . The film according to  claim 7  wherein: 
 said fourth nanoparticle dispersion has a red luminescence.  
 
     
     
         10 . The film according to  claim 1  wherein: 
 between approximately 5 to 10 nanoparticle bilayers of each of said dispersions comprise said film.  
 
     
     
         11 . A method of layer-by-layer assembly of nanoparticles comprising the steps of: 
 a. placing a slide into a polyelectrolyte solution;    b. rinsing said slide;    c. immersing said slide into a solution of PAA, thereby forming a polyelectrolyte/PAA substrate layer for rendering a surface of said slide more uniform to provide better adsorption of subsequent nanoparticle layers;    d. exposing said surface of said substrate to a nanoparticle dispersion;    repeating steps a-d until a desired number of nanoparticle bilayers are deposited on said substrate;    exchanging said nanoparticle dispersion for a second nanoparticle dispersion having nanoparticles of a different size; and    repeating above steps as desired.    
     
     
         12 . The method according to  claim 11  wherein: 
 said step of placing said slide into a polyelectrolyte solution comprises placing said slide into PDDA.  
 
     
     
         13 . The method according to  claim 11  wherein: 
 said step of exposing said surface of said substrate to a nanoparticle dispersion comprises exposing said surface of said substrate to a CdTe nanoparticle dispersion.  
 
     
     
         14 . The method according to  claim 11  wherein: 
 said step of exchanging said nanoparticle dispersion for a second nanoparticle dispersion having nanoparticles of a different size comprises exchanging said nanoparticle dispersion for a second nanoparticle dispersion having nanoparticles of a larger size, whereby an addition of layers having increasing diameter results in a shift of luminescence of the assembly toward a red part of an optical spectrum.  
 
     
     
         15 . The method according to  claim 11  further comprising: 
 repeating steps a-d until a luminescence spectrum from a stack of four nanoparticle diameters has a plateau appearance reflecting approximately equal emission intensity in a wide range of wavelengths.